Method and apparatus for conformal embedded ceramic armor

ABSTRACT

Armor and a method of making the same, where ceramic tile is placed in  opngs of a frame of material and layers of material are in contact with opposite sides of the frame and the tile, and wherein the material of both the frame and the layers is passed through a superplastic state by applications of heat and pressure.

GOVERNMENT INTEREST

The invention described herein may be manufactured, used, and licensedby or for the Government for governmental purposes without the paymentto me of any royalty thereon.

FIELD OF THE INVENTION

This invention is in the field of armor for protection againstprojectiles.

BACKGROUND OF THE INVENTION

In view of their possessing greater hardness, higher strength and lowerdensity than metals it would seem that ceramic materials could be usedin fabricating armor. Unfortunately, however, they have very low tensilestrengths that make them vulnerable to any residual or tensile stressesdeveloped during manufacture, or in defeating a projectile, that causethem to crack so as to be ineffective as armor. The present methods ofensuring that ceramics in armor will not experience tensile stresses arenot reliable, are often very cumbersome and costly to implement andgenerally entail resorting to complicated structures not readilyconformable to the shape of the vehicle or structure that needs theprotection. One procedure calls for precision machined ceramic tiles andcavities in armor metal blocks. The ceramic filled cavities are thencovered over with a top plate which is then generally welded to thearmor metal block. Normal temperature excursions and differences inthermal expansion coefficients between the ceramic and the surroundingmetal will open up a gap between these materials. Reflected tensilestresses will arise within the ceramic at this gap during ballisticimpact and thereby normally lead to degraded performance of the ceramic.

Other procedures may take extensive effort to ensure that the ceramicmaterial is in a compressive state by either wrapping the ceramicmonoblocks in fiber reinforced organic composite casings before placingin the metal armor cavities, or by packing/pouring sealant compounds inthe air gaps before sealing up the armor blocks. These techniques oftrying to ensure that no tensile stresses are generated are also notreliable, very time consuming to implement, and ballisticallyinefficient. Resorting to another procedure, that of casting the metalaround the ceramic often leads to shrinkage gaps at the ceramicmonoblocks upon cooling the casting. Good processing control to fullyeliminate these types of gaps have so far been difficult to establish.It is well known that certain metals as well as ceramics having finegrain structure can be made to exhibit what is called a superplasticproperty; i.e. it is pliant, by applying proper amounts of strain whilewithin a given range of temperatures. Using a superplasticpreconditioned 7475 aluminum alloy as an example, superplasticity can bemade to occur by heating it to a temperature between 510° C. and 520° C.and slowly applying pressure at 0.05 MPa/minute that corresponds to asuperplastic strain rate of 0.0001/seconds until a maximum pressure of0.7 MPa is reached. The alloy is then cooled to room temperature whilethe maximum pressure is maintained. A pressure of 1000 p.s.i. equals 6.9MPa's (megapascals). Other materials require different pressures andtemperatures. In accordance with this invention ceramic tiles arelocated within openings formed in a layer of material, hereinafterreferred to as a picture frame that exhibits superplasticity whensubjected to appropriate strain while at an appropriate temperature.Preferably, layers of like material are placed in contact with oppositesides of the tiles and the picture frame so as to form an assembly inwhich the tiles are completely enclosed.

An aspect of this invention is the maintenance of the maximum pressurefor a period of time so as to permit improved diffusion bonding of theouter layers to the tile and the picture frame. The bonding to the tilecan be improved by first subjecting the tile to ion implantation orplasma enhanced coating procedures so as to provide a metallic surface.

Another aspect of this invention is to subject the assembly to furtherheat treatment to convert the SPF (superplastic forming) microstructureof the material of the picture frame and the layers into a higherstrength microstructural form. This provides additional armor protectionwithout any loss of mass efficiency. This post heat treatmenttemperature is less than that used in creating the superplasticcondition to ensure that there is no diminution of the compressivestress on the embedded ceramic tile,

A less preferable armor structure of this invention that is still betterthan the prior art is one in which the outer layers of the assembly areeliminated in which case the pressure is applied by gas to an assemblythat is enclosed within an evacuation bag.

One of the significant advantages of this invention is the fact thattile is embedded in metal that can be bent so as to provide a desiredshape. The required procedures are performed to create the requiredcompressive forces on the tile that eliminate tensile forces that mayresult from the impact of a penetrator. This result obtains because themetal is such that it acquires a superplastic state when subjected tochanging pressure at a desired temperature. When in this state, themetal becomes intimately connected to the tile, and contractive forcesoccur as it is cooled down.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are described below with referenceto the drawings, in which like items are indicated by the same referencedesignation, wherein:

FIG. 1 is an exploded isometric view of an assembly in which tile isembedded in accordance with this invention;

FIG. 2 is a cross section taken along 2--2 of the assembly of FIG. 1when the components of FIG. 1 are compressed together;

FIG. 3 is a cross section of an assembly having tile embedded therein inaccordance with this invention illustrating an angular surface formedtherewith; and

FIG. 4 is a cross section of layers of assemblies having tile embeddedtherein in accordance with this invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, the exploded isometric view of an assembly of the inventionshows a picture frame 2 having a number of rectangular openings 4,6,8,and 10 therein into which tiles 12,14,16, and 18 are respectivelyadapted to fit. Layers 20 and 22 are on opposite sides of the pictureframe 2. Channel 24 is formed in the bottom of the picture frame 2 so asto communicate with the openings 6 and 8, and another channel 26 isformed in the bottom of the picture frame 2 so as to communicate withthe opening 4 and 10. Similarly, a channel 28 in the top of the pictureframe 2 communicates with the openings 6 and 8, and a channel 30 in thetop of the picture frame 2 communicates with the openings 4 and 10.

When the components of FIG. 1 are vertically compressed together, across section 2--2 of FIG. 1 will appear as shown in FIG. 2, wherein thelayers 20 and 22 are in intimate contact with the picture frame 2 andthe ceramic tiles 4,6,8, and 10.

The material from which the picture frame 2 and the layers 20,22 aremade is such that it will produce a superplastic state when at aselected temperature and subjected to increasing pressure. When in thisstate, the material flows like gum so that pressure supplied to thelayers 20 and 22 by a press brings them into intimate contact with thesurface of the tiles and forces the picture frame 2 into intimatecontact with the edges of the tiles. When the temperature is reduced toambient and the pressure is removed, the intimate contact is maintained.This is important because gaps tend to permit tensile forces to beapplied to the tile by the impact of a projectile, and because tile hasa low tensile strength, it breaks up.

Metals such as aluminum and steel as well as ceramic are known toexhibit superplastic properties. Any material having this capability canbe used in the invention. The material is also available in powderedform.

During the process, air that might otherwise interfere with the bondingof the tile to the picture frame 2 and the layers 20 and 22 is withdrawnby coupling a vacuum pump to the channels 24,26,28, and 30.

In accordance with an aspect of the invention, the bonding between thetiles 4,6,8, and 10 to the metallic material of the picture frame 2 andthe layers 20 and 22 is improved by metallizing the surfaces of the tileby well known ion implantation or plasma enhanced coating techniques.

Reference is made to FIG. 3 showing an assembly of this invention thatis bent about an axis 34 that lies between tiles 36 and 38 so as to forma section 40 having tiles 36 and 42 embedded therein that is at an anglewith respect to a section 44 having tiles 38 and 46 embedded therein. Ifthe armor is to have a gradually curved surface, the tiles can be madeto have a reduced dimension in at least the direction along the curve soas to form a series of small chords. In addition, the outer surfaces ofthe assembly could be subjected to the pressure required by the processby a press having curved surfaces. Alternatively, the structure could bebent to the desired curvature and placed in an evacuated bag that issubjected to air pressure.

In order to simplify the drawings, an assembly embodying the inventionhas been shown in FIG. 1 to be comprised of a single layer of ceramictile, but in order to armor the spaces between tiles, multiple layers oftile such as 48, 50, and 52 of FIG. 4 are used. In making thisstructure, only one layer such as 20 or 22 of FIG. 1 is between thelayers 48 and 50 and 50 and 52.

What is claimed is:
 1. A method for forming armor comprising:forming anassembly by surrounding at least one ceramic tile with material thatbecomes superplastic when it is subjected to increasing pressure whileat a selected temperature; heating the assembly to a given temperature;subjecting the assembly to a pressure that increases to a given value;maintaining said given temperature and said given pressure for a periodof time; reducing the temperature while maintaining the given pressure;and removing the pressure.
 2. A method as set forth in claim 1,wherein:a vacuum is drawn around the ceramic tile.
 3. A method as setforth in Claim 1, further comprising:heating said assembly a second timeto a second given temperature; water quenching the assembly; and agingthe assembly by maintaining it at a third temperature for a secondperiod of time.
 4. A method as set forth in claim 1 wherein saidmaterial is metal.
 5. An armor assembly comprising:a frame of materialhaving a plurality of openings; a plurality of ceramic tiles in each ofsaid openings, respectively; layers of material in contact with eachside of said frame and said ceramic tiles; and said frame and saidlayers being comprised of material that has been subjected to heat andpressure so that they have passed through a superplastic forming anddiffusion bonding state.
 6. An armor assembly comprising:material thathas been passed through a superplastic state; and ceramic tile embeddedin said material.
 7. An armor assembly as set forth is claim 6, whereinsaid tile has been metallized before it was embedded.